Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute , University of Minnesota , Minneapolis , Minnesota 55455-0431 , United States.
J Chem Theory Comput. 2018 Apr 10;14(4):2017-2025. doi: 10.1021/acs.jctc.8b00032. Epub 2018 Mar 14.
Multireference methods such as multistate complete active space second-order perturbation theory (MS-CASPT2) and multiconfiguration pair-density functional theory (MC-PDFT) can be very accurate, but they have the disadvantage that they are not black-box methods, and finding a good active space for the reference wave function often requires nonsystematic procedures based on intimate knowledge of the system under study. In this paper, we propose a scheme called the ABC scheme, which is a three-step calculation using three parameters, for automatic selection (without looking at the orbitals and without using any knowledge of the specific system at hand) of the active space (including both the size of the active space and the orbitals in the active space) for MS-CASPT2 or MC-PDFT calculations, and we report tests of the scheme on the first five excitation energies for a set of ten doublet radicals. The results show that the ABC scheme is very successful for both MS-CASPT2 and MC-PDFT for all ten systems considered here.
多参考方法，如多态完全活性空间二级微扰理论（MS-CASPT2）和多组态对密度泛函理论（MC-PDFT），可以非常准确，但它们的缺点是它们不是黑盒方法，并且为参考波函数找到一个好的活动空间通常需要基于对所研究系统的深入了解的非系统程序。在本文中，我们提出了一种称为 ABC 方案的方案，该方案是一个三步计算，使用三个参数，用于自动选择（不查看轨道且不使用手头特定系统的任何知识）用于 MS-CASPT2 或 MC-PDFT 计算的活性空间（包括活性空间的大小和活性空间中的轨道），并报告了该方案在十组双自由基的前五个激发能上的测试结果。结果表明，对于这里考虑的所有十个系统，ABC 方案对于 MS-CASPT2 和 MC-PDFT 都非常成功。
